batman-adv: Check ptr for NULL before reducing its refcnt

commit 6340dcbd619450c1bb55eb999e554e4f0e6dab0a upstream.

The commit b37a46683739 ("netdevice: add the case if dev is NULL") changed
the way how the NULL check for net_devices have to be handled when trying
to reduce its reference counter. Before this commit, it was the
responsibility of the caller to check whether the object is NULL or not.
But it was changed to behave more like kfree. Now the callee has to handle
the NULL-case.

The batman-adv code was scanned via cocinelle for similar places. These
were changed to use the paradigm

  @@
  identifier E, T, R, C;
  identifier put;
  @@
   void put(struct T *E)
   {
  +	if (!E)
  +		return;
  	kref_put(&E->C, R);
   }

Functions which were used in other sources files were moved to the header
to allow the compiler to inline the NULL check and the kref_put call.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/batman-adv/network-coding.c

@@ -222,6 +222,9 @@ static void batadv_nc_node_release(struct kref *ref)
  */
 static void batadv_nc_node_put(struct batadv_nc_node *nc_node)
 {
+	if (!nc_node)
+		return;
+
 	kref_put(&nc_node->refcount, batadv_nc_node_release);
 }
 
@@ -246,6 +249,9 @@ static void batadv_nc_path_release(struct kref *ref)
  */
 static void batadv_nc_path_put(struct batadv_nc_path *nc_path)
 {
+	if (!nc_path)
+		return;
+
 	kref_put(&nc_path->refcount, batadv_nc_path_release);
 }